1. Field of the Invention
The present invention relates to an air bag device including an inflator accommodated in a retainer to which a peripheral edge of an opening of a folded-up air bag is fixed, so that the air bag is deployed by a gas generated by the inflator upon collision of a vehicle to restrain an occupant, wherein a vent hole defined in the retainer is opened and closed by a control valve operated by an actuator.
2. Description of the Related Art
In a conventional air bag device, a vent hole is provided in an air bag, which is expanded by a gas generated by an inflator, so that a portion of the gas is discharged through the vent hole to control the internal pressure in the air bag. There is such a proposed air bag device, which is designed so that a vent hole is previously closed by a thin membrane, whereby an air bag is expanded promptly at an initial stage of the deployment of the air bag, and when the internal pressure in the air bag is raised after completion of the deployment, the thin membrane is broken to permit a gas to be discharged through the vent hole, thereby softly restraining an occupant (see Japanese Utility Model Registration Publication No.5-6206).
There is also such a proposed air bag device, which includes two inflators is designed so that when no occupant exists in the vicinity of the air bag device, both of the two inflators are ignited, whereas when an occupant exists in the vicinity of the air bag device, only one of the inflators is ignited, whereby the speed of deployment of and the internal pressure in an air bag are controlled in accordance with the position of the occupant (see Japanese Patent Application Laid-open No.9-301115).
The air bag device described in the above Japanese Utility Model registration Publication No.5-6206 suffers from a problem that a scattering is liable to be generated in pressure breaking the thin membrane and for this reason, it is difficult not only to properly open the vent hole at the time when the internal pressure in the air bag reaches a predetermined value, but also to accurately control the internal pressure, because the vent hole once opened cannot be closed. The air bag device described in the above Japanese Patent Application Laid-open No.9-301115 suffers from a problem that the two inflators are required, not only resulting in an increased number of parts, causing an increase in cost, but also the characteristic of deployment of the air bag can be controlled at two stages only and for this reason, it is difficult to carry out a fine control.
Therefore, there is a proposed air bag device, in which a vent hole is defined in a housing having an inflator accommodated therein, so that the speed of deployment of and the internal pressure in an air bag are finely controlled by opening and closing the vent hole by a control valve operated by a motor (see Japanese Utility Model No.3042312).
However, the air bag device proposed in Japanese Utility Model No.3042312 suffers from a problem that a single valve member of a control valve is operated by the motor to open and close the vent hole and for this reason, to ensure a sufficient opening degree of the control valve, it is necessary to operate the valve member by a large-sized motor to a large extent, thereby bringing about an increase in cost and an increase in size of the air bag device.
When a piezoelectric element is employed as an actuator for opening and closing the valve member, a load produced by the piezoelectric element and the amount of piezoelectric element flexure are in inverse proportion to each other. For this reason, when a large-sized piezoelectric element is employed to open and close a large-size valve member, not only the cost is increased, but also there is a possibility that the amount of piezoelectric element flexure may be insufficient, resulting in an insufficient opening degree of the control valve.
Therefore, there is an air bag device proposed by the present applicant, in which a vent hole is defined in a retainer having an inflator accommodated therein, so that the speed of deployment of and the internal pressure in an air bag are finely controlled by opening and closing the vent hole by a control valve operated by an actuator (see Japanese Patent Application No.10-143781).
In the air bag device proposed in the above Japanese Patent Application No.10-143781, when the vent hole is closed to be covered from the outside by the valve member formed of an elastomeric material, the valve member can be flexed outwards by the pressure of a high-pressure gas ejected into the retainer by the inflator, thereby automatically opening the vent hole. In this case, however, the following problem is encountered: It is difficult to set the elasticity of the valve member and the pressure receiving area, and to open the valve member with an appropriate timing and at an appropriate opening degree.
In addition, the air bag device proposed in the above Japanese Patent Application No. 10-143781 includes a control valve having a piezoelectric element which is adhered to a protector made of a strip-shaped metal and having the same shape as the protector, so that the protector is curved along with the piezoelectric element by supplying current to the piezoelectric element, thereby opening the vent hole. However, the control valve is not provided with a means for limiting the maximum opening degree of the control valve and for this reason, there is a possibility that the control valve may be over-flexed to a large extent, resulting in an excessive opening degree, or the brittle piezoelectric element may be excessively deformed and thus damaged.
Accordingly, it is a first object of the present invention that the opening degree of a control valve for opening and closing a vent hole in an air bag device can be ensured at a sufficient level by use of a small-sized and inexpensive actuator.
It is a second object of the present invention to ensure that when the valve member of the control valve covering the vent hole in an air bag device from the outside is formed from an elastomeric material, the opening degree of the control valve can be controlled appropriately.
It is a third object of the present invention to provide an air bag device including a control valve capable of opening and closing a vent hole defined in a retainer, wherein a valve member of the control valve can be prevented from being excessively deformed.
To achieve the above first object, according to a first aspect and feature of the present invention, there is provided an air bag device including an inflator accommodated in a retainer to which a peripheral edge of an opening of a folded-up air bag is fixed, so that the air bag is deployed by a gas generated by the inflator upon collision of a vehicle to restrain an occupant, and a control valve operated by an actuator for opening and closing a vent hole defined in the retainer, the control valve including a plurality of divided valve members.
With the above arrangement, the speed of deployment of the air bag, the magnitude of the restraining force provided by the air bag, the speed of contraction of the air bag and the like can be determined at any values in accordance with the state of the collision and the state of an occupant by controlling the opening degree of the vent hole for escape of the high-pressure gas, when the air bag is deployed by the high-pressure gas generated by the inflator. The control valve has the plurality of divided valve members and hence, even if the size of the actuator for operating each of the valve members is reduced to provide a reduction in cost, a sufficient opening degree of the entire control valve can be ensured.
To achieve the first object, according to a second aspect and feature of the present invention, in addition to the first feature, the actuator is a piezoelectric element.
With the above arrangement, the size of the actuator can be reduced remarkably by employment of the piezoelectric element.
To achieve the first object, according to a third aspect and feature of the present invention, in addition to the first feature, the plurality of valve members are curved and opened, the direction of curving of at least one of the valve members being different from that of the remaining valve members.
To achieve the second object, according to a fourth aspect and feature of the present invention, there is provided an air bag device including an inflator accommodated in a retainer to which a peripheral edge of an opening of a folded-up air bag is fixed, so that the air bag is deployed by a gas generated by the inflator upon collision of a vehicle to restrain an occupant, a control valve operated by an actuator for controlling an opening degree of a vent hole defined in the retainer, the control valve including a valve member which is formed of an elastomeric material and supported to cover the vent hole from the outside, so that when the vent hole is opened by a gas generated by the inflator, the actuator selectively generates a load in a direction to close or open the vent hole by the valve member.
With the above arrangement, the speed of deployment of the air bag, the magnitude of the restraining force provided by the air bag, the speed of contraction of the air bag and the like can be determined at any values in accordance with the state of the collision and the state of an occupant by controlling the opening degree of the vent hole for escape of the high-pressure gas, when the air bag is deployed by the high-pressure gas generated by the inflator. When the valve member formed of the elastomeric material is flexed and opened by the pressure of the gas generated by the inflator, the opening degree of the valve member can be controlled appropriately by supplying current to the actuator to generate a load in a direction to inhibit the opening of the valve member, or by supplying current to the actuator to generate a load in a direction to promote the opening of the valve member of the control valve.
To achieve the third object, according to a fifth aspect and feature of the present invention, there is provided an air bag device including an inflator accommodated in a retainer to which a peripheral edge of an opening of a folded-up air bag is fixed, so that the air bag is deployed by a gas generated by the inflator upon collision of a vehicle to restrain an occupant, a control valve having a valve member operated by an actuator for opening and closing a vent hole defined in the retainer, and a stopper for limiting the maximum opening degree of the valve member of the control valve.
With the above arrangement, the speed of deployment of the air bag, the magnitude of the restraining force provided by the air bag, the speed of contraction of the air bag and the like can be determined at any values in accordance with the state of the collision and the state of an occupant by controlling the opening degree of the vent hole for escape of the high-pressure gas, when the air bag is deployed by the high-pressure gas generated by the inflator. In addition, the maximum opening degree of the valve member of the control valve is limited by the stopper and hence, it is possible to prevent the valve member from being flexed to a large extent by the pressure of the high-pressure gas flowing through the vent hole, resulting in an excessive opening degree, and to prevent the actuator from being excessively deformed and thus damaged.
To achieve the third object, according to a sixth aspect and feature of the present invention, in addition to the fifth feature, a seal member is mounted on at least one of a valve seat formed at a peripheral edge of the vent hole and the valve member seated on the valve seat.
With the above arrangement, the valve member and the valve seat at the peripheral edge of the vent hole are put into abutment against each other with the seal member interposed therebetween and hence, it is possible to reliably prevent the high-pressure gas from being leaked from a gap between the vent hole and the valve seat.
To achieve the third object, according to a seventh aspect and feature of the present invention, in addition to the fifth feature, a projection is provided around the periphery of the vent hole and adapted to abut against the outer periphery of the valve member to position the valve member relative to the vent hole.
With the above arrangement, the valve member can be mounted at a proper position relative to the vent hole by bringing the projection provided around the periphery into abutment against the outer periphery of the valve member to position the valve member relative to the vent hole.
To achieve the third object, according to an eighth aspect and feature of the present invention, in addition to the fifth feature, the actuator comprises a piezoelectric element adhered to the valve member, and the valve member is provided with an opening in which an adhesive is provided in order to increase the strength of adhesion between the valve member and the actuator.
With the above arrangement, the piezoelectric element is adhered to the valve member provided with the opening and the adhesive and hence, the valve member and the piezoelectric element can be adhered firmly to each other.